Within the framework of research on DNA stability systems, the Rotterdam team has generated a comprehensive series of mouse mutants with defined defects in DNA repair and cell cycle control pathways. Several of these mice (and parallel human syndromes) display features of premature aging. Within this program we would like to employ this collection of mouse mutants as a model for systematic investigation of the contribution of each of the genome stability systems to (prevention of) senescence. More specifically in these mice we will (1) assess levels of the spontaneous DNA lesions 8-OhdG and interstrand and interstrand cross links; (2) develop a new transgenic assay system, that measures transcription- interference at a single cell level, using GFP and puromycin resistance genes, under the control of the prokaryotic tet-repressor; and (3) analyse mouse tissues for chromosomal aberrations and aneuploidy using FISH techniques. Finally, if time permits we will analyse the expression profiles of young and senescent fibroblasts from different repair mutants, using the SAGE method.